Ursids

For the bear family, see Ursidae.

Ursids (URS)
Ursa Minor with the radiant of the Ursids marked in red
Parent body	8P/Tuttle
Radiant
Constellation	Ursa Minor (near Kochab)
Right ascension	14h 36m
Declination	+75.3° (Northern Hemisphere)
Properties
Occurs during	December 17 – December 26
Date of peak	December 22
Velocity	33 km/s
Zenithal hourly rate	10

The Ursid (URS) meteor activity begins annually around December 17 and runs for over a week, until the 25th or 26th. This meteor shower is named for its radiant point, which is located near the star Beta Ursae Minoris (Kochab) in the constellation Ursa Minor.

History

The Ursids were probably discovered by William F. Denning, who observed them for several years around the start of the 20th century. While there were sporadic observations after, the first coordinated studies of the shower didn't begin until Dr. A. Bečvář observed an outburst of 169 per hour in 1945. Further observations in the 1970s and ongoing to current have established a relationship with comet 8P/Tuttle. Peter Jenniskens and Esko Lyytinen discovered that outbursts could happen when comet Tuttle was at aphelion because some meteoroids get trapped in the 7/6 orbital resonance with Jupiter.

Technical information

Earlier observations described an average radiant of RA=217°, DEC=76°, with maximum occurring at a solar longitude of 270.66 deg (about December 22), with the duration being established as December 17–24.

The Ursids have a particularly narrow stream, prompting veteran meteor observer, Norman W. McLeod, III (Florida) to comment that the Ursids "must be a compact stream like the Quadrantids. You have to be within 12 hours of maximum to see much."

External links

• Gary Kronk's Meteor Showers Online - Ursids
• International Meteor Organisation Calendar - Fall 2005
• NASA Ursid Airborne Campaign (2008 + Java applet)
• 2011 Ursids Radio results (RMOB)
• Ursids at Constellation Guide